Gestational diabetes mellitus (GDM) has escalated to epidemic proportion and can cause maternal and child complications. GDM is a significant maternal risk factor for subsequent development of type 2 diabetes (T2D) and places the fetus at increased risk for congenital morbidity/mortality and for future onset of diabetes. American Indian and Alaska Native (AI/AN) women are twice as likely to develop GDM and T2D; mostly due to healthcare disparities (e.g., limited access to resources, lack of culturally relevant programs). The need for an inexpensive accessible GDM intervention in this population is compelling. The intervention should be delivered during adolescence and prior to sexual debut. Preconception counseling (PC) prevents unplanned pregnancies and significantly reduces risks of complications. If GDM in a previous pregnancy is an indicator of high risk in subsequent pregnancies, then preventing GDM in a first pregnancy is imperative. For a significant and innovative shift in paradigm, we propose a primary prevention PC intervention for AI/adolescent females at risk for GDM to enhance healthy lifestyle behaviors and family planning vigilance prior to this first pregnancy. We will target girls starting at the age of 12 to coincide with boththe Coming-of-Age rituals for AI/AN girls during which many receive womanly advice from elder female family members, and the American Diabetes Association recommendation that PC in all females should start at puberty. This new directive will require support from the teens mothers (or their female caregiver) and well-informed community health care professionals (HCP). Our objective is to adapt our current PC intervention (validated for teens with diabetes) using a sequential mixed-method design with a multi-tribal AI/AN community-based participatory research (CBPR) approach (e.g., Navajo, Cherokee, 40 Oklahoma tribes; 8 project members are AI/AN) by first using focus groups of teens, mothers, HCP, and Tribal leaders; and then testing this culturally appropriate PC theory-based intervention named STOP-GDM in AI/AN adolescent females 12 to <20yrs at risk for GDM (e.g., pre-diabetes or BMI> 85%). Teens and their mothers will receive STOP-GDM to raise their awareness of the risks of GDM and benefits of healthy lifestyle to reduce these risks. By also providing mothers with PC knowledge and skills they can naturally weave cultural/social influences into their communications with their daughters. The multi-level intervention will be directed at the individual, familial and institutioal levels simultaneously. AI/AN community-researcher partnerships have been established. A randomized controlled trial with a 15mos follow-up will test the effects of receiving online STOP-GDM on mother-daughter (M-D) cognitive/psychosocial and behavioral outcomes, and daughter family planning vigilance. The final online STOP- GDM program will be provided at no cost to the Indian Health Service (IHS) for dissemination to all their sites. HCPs at each clinical facilit will be given free access to a continuing education program for PC training. This proposal provides a unique opportunity for a broad dissemination to significantly impact all IHS AI/AN female teens at risk for GDM, and help to prevent them and their future children from developing T2D.